Induction heating devices have been available for many years, including some that raise the temperature of susceptors containing metallic substances that have eddy currents induced therein when receiving the magnetic field produced by a work coil of the induction heating device. Some of these induction heating devices have been used to connect two sections of pipe together; in some cases the induction heating devices solder the pipe sections together, or even to weld the pipe sections together, in certain high-powered induction devices.
One example induction heating device is disclosed in U.S. Pat. No. 5,374,808 and is used with a “pull test” machine that has a stationary chuck and a moveable chuck that pulls apart two test pieces that previously have been bonded together. The induction heating device has a U-shaped core or “pole piece” that consists of two spaced-apart opposite ends that define an air gap therebetween. An induction coil is wrapped around the U-shaped pole piece, thereby forming an induction coil with a magnetic core. A capacitor is connected to opposite ends of the induction coil to create a tank circuit, and a power oscillator can be used to adjust the power level and frequency of electrical energy that is supplied to the tank circuit. In general, this induction heating device is used to test the strength of two thermally non-conductive test pieces that have been bonded together. It is not being used to solder or weld two pieces together.
Another patent, U.S. Pat. No. 5,412,184, discloses an induction heating tool that is shaped like a jaw-like cylinder. The jaws contain electrical conductors that provide inductive heat (as a magnetic field) when energized, and the jaws have a curved cross-section that brings the two edges of the jaw-like structure into contact after being wrapped around a pipe or other cylindrical object that is to be heated. There are inner surface and outer surface conductors that are connected in a manner so that their current flows will be in opposite directions to reduce the electromagnetic radiation that is external to the device. One of the embodiments (see FIG. 7) uses a pistol grip to pull the jaws together around the pipe to be heated.
Another patent, U.S. Pat. No. 5,350,902, discloses an induction heating device that has a handle with a hollow interior, a “wrist” connected to one end of the handle, a U-shaped pole piece having two spaced-apart ends, a tank circuit including an induction coil wrapped around the pole piece, and a capacitor connected to the induction coil. There is also a “head” connected to the wrist that includes a housing for receiving the U-shaped pole piece, in which the two spaced-apart ends of the pole piece extend outwardly beyond the housing. A susceptor is to be placed in juxtaposition to the ends of the U-shaped pole piece, and the susceptor is heated by magnetic flux passing between the two ends of the pole piece. The wrist provides an articulating mount for the head, in which the wrist provides multiple degrees of freedom of motion so the head can swivel about two joints, which are essentially ball and socket members.
U.S. Pat. No. 5,786,575 discloses a “wrap tool” that has first and second coil regions and flange regions for inducing oscillating magnetic fields to fuse a plastic coupling to a substrate. The flange regions of the wrap tool open to receive a pipe, and then close to surround the pipe before a heating event, in which the pipes will be melted and fused together.
U.S. Pat. No. 4,521,659 discloses an induction heating gun that can fuse thermoplastics using an alternating current that passes through a tank circuit, in which the inductor member of the tank circuit is wrapped around a curved pole piece of a ferromagnetic material. The magnetic flux in the induction coil flows to the ends of the pole piece and into a screen placed between the materials to be joined, and the flux induces a current in the screen which generates heat to melt the thermoplastics together.
U.S. Pat. No. 3,428,769 discloses an induction heating tool for welding or brazing tubes, in which the heating tool has an overall shape of a pliers-type tool that clamps around the tube to be heated. The clamping action is by use of two separate jaws.
Published patent application number US 2003/0226838 A1 discloses a magnetic welder that provides an induction coil to heat a set of metal workpieces sufficiently to form a weld bond. The induction coil has a movable element that, when “opened,” forms a gap to allow the coil to be placed over the workpieces, and after the coil has been moved into position, the movable element “closes” to circumscribe the workpieces. The magnetic welder exhibits an insulated handle that includes a trigger that actuates the magnetic field. The induction coil can also have a locking mechanism that may be used to lock the coil in its closed position.
Some of the conventional inventions use flexible coil members to allow the induction coil to be essentially “wrapped” around the workpiece, or to be bent into a desired shape with respect to a workpiece. Patents describing such an arrangement include U.S. Pat. No. 6,346,690, U.S. Pat. No. 5,412,184 (noted above), U.S. Pat. No. 5,352,871, U.S. Pat. No. 5,266,764, U.S. Pat. No. 5,113,049, U.S. Pat. No. 4,695,712, U.S. Pat. No. 4,388,510, and U.S. Pat. No. 3,260,792.
Others of the conventional inventions use coils that are liquid-cooled, in which the induction coil is hollow, and a cooling fluid is directed through the hollow coil to take heat away from the energized coil. Patents describing such an arrangement include U.S. Pat. Nos. 4,271,345 and 3,365,563.
As noted above, there are several conventional inventions that use an induction coil that “opens” to receive a workpiece (as a “side-entry”), and then “closes” to essentially surround the workpiece for the heating event. Other patents describing such an arrangement include U.S. Pat. No. 5,874,713, U.S. Pat. No. 5,786,575, and U.S. Pat. No. 3,365,563.
One variation if the conventional inventions is a side-entry induction coil, in which the coil itself does not necessarily move to allow a workpiece to be inserted into a heating area or heating zone. However, a “flux concentrator” is provided at the mouth of the coil which is made of ferrite material, and which is movable between a “loading” position (i.e., an open position) and a “heating position” (i.e., a closed position). This arrangement is disclosed in U.S. Pat. No. 5,630,958. This arrangement is different than the movable coil inventions; nevertheless there is a movable magnetic circuit member that has an open position and a closed (heating) position.
It would be an improvement to provide an induction heating tool that is capable of soldering or brazing metal pipes together without force-cooling liquid running through the induction coil conductors, or alternatively using heat pipes as the induction coil conductors, and moreover by using a very portable induction heating tool in which the induction coil is easily placed around portions of a cylindrical object (such as two pipes), without having to “wrap” or “close” the induction coil windings around the pipes, and without needing a separate magnetic circuit member to be moved from an open (loading) position to a closed (heating) position.